Apparatus for performing modulo arithmetic with three-port adder

A method for calculating an address from a first, second and third values comprising the steps of:

• first, adding said first, second and third values in a two stage adder, said two stage adder including a first stage adder for outputting an intermediate carry;
• second, determining in a logic unit coupled to said two stage adder if an intermediate carry in said first step results from the addition of said first and second values;
• and
• third, modifying said intermediate carry inn said logic unit if said second step determines said intermediate carry results from the addition of said first and second values.

A method for calculating an address from a first, second and third values comprising the steps of:

• adding said first and second values in a single stage adder, said single stage adder outputting a first intermediate carry;
• adding said first, second and third values in a two stage adder, said two stage adder including a first stage adder for outputting a second intermediate carry and a second stage adder for outputting a sum, wherein said first value is a base address, said second value is a displacement, sad said third value is a segment base value;
• providing as inputs to a logic unit coupled to said two stage adder said first and second intermediate carries;
• determining if said second intermediate carry results from the addition of said first and second values;
• and
• third, modifying said second intermediate carry if said determining step determines said second intermediate carry results from the addition of said first and second values.